Googstr/extension/background.js

// Goostr signer — background service worker.
//
// Holds the nostr key in chrome.storage.session (memory only, cleared when the
// browser quits) and answers NIP-07 requests from web pages, asking the user
// before a site may use it. The key arrives from the Goostr website via
// externally_connectable messaging — only origins listed in manifest.json can
// send it.

import { getPublicKey, finalizeEvent, nip04, nip19, nip44, hexToBytes } from "./vendor/nostr-tools.js";
import { GOOSTR_URL } from "./config.js";

const PROMPT_W = 380;
const PROMPT_H = 560;

async function getKey() {
  const { sk } = await chrome.storage.session.get("sk");
  return sk ? hexToBytes(sk) : null;
}

async function getPerms() {
  const { perms } = await chrome.storage.local.get("perms");
  return perms || {}; // origin -> "always"
}

async function setBadge() {
  const sk = await getKey();
  await chrome.action.setBadgeText({ text: sk ? "" : "off" });
  await chrome.action.setBadgeBackgroundColor({ color: "#6d28d9" });
}
chrome.runtime.onStartup.addListener(setBadge);
chrome.runtime.onInstalled.addListener(setBadge);

// ---------- messages from the Goostr website ----------

chrome.runtime.onMessageExternal.addListener((msg, sender, respond) => {
  (async () => {
    switch (msg?.type) {
      case "status": {
        const sk = await getKey();
        return { installed: true, version: chrome.runtime.getManifest().version, pubkey: sk ? getPublicKey(sk) : null };
      }
      case "setKey": {
        if (!/^[0-9a-f]{64}$/.test(msg.sk || "")) throw new Error("bad key");
        await chrome.storage.session.set({ sk: msg.sk, profile: msg.profile || null, from: sender.origin });
        await setBadge();
        return { ok: true, pubkey: getPublicKey(hexToBytes(msg.sk)) };
      }
      case "lock":
        await chrome.storage.session.remove(["sk", "profile"]);
        await setBadge();
        return { ok: true };
      default:
        throw new Error("unknown message");
    }
  })().then(respond, (e) => respond({ error: String(e.message || e) }));
  return true;
});

// ---------- permission prompts ----------

const pending = new Map(); // id -> { resolve, windowId }

function askUser(request) {
  return new Promise(async (resolve) => {
    const id = crypto.randomUUID();
    await chrome.storage.session.set({ [`prompt:${id}`]: request });
    const win = await chrome.windows.create({
      url: `prompt.html?id=${id}`,
      type: "popup",
      width: PROMPT_W,
      height: PROMPT_H,
    });
    pending.set(id, { resolve, windowId: win.id });
  });
}

function settle(id, decision) {
  const p = pending.get(id);
  if (!p) return;
  pending.delete(id);
  chrome.storage.session.remove(`prompt:${id}`);
  p.resolve(decision);
}

// An open port from prompt.html keeps this worker alive while the user decides.
chrome.runtime.onConnect.addListener(() => {});

chrome.windows.onRemoved.addListener((windowId) => {
  for (const [id, p] of pending) if (p.windowId === windowId) settle(id, "deny");
});

// ---------- NIP-07 ----------

async function nip07(method, params, origin) {
  let sk = await getKey();
  const perms = await getPerms();

  if (!sk || perms[origin] !== "always") {
    const decision = await askUser({ origin, method, params, locked: !sk });
    if (decision === "deny") throw new Error("Rejected by user");
    if (decision === "always") {
      const fresh = await getPerms();
      fresh[origin] = "always";
      await chrome.storage.local.set({ perms: fresh });
    }
    sk = await getKey(); // the prompt may have unlocked us
    if (!sk) throw new Error("Goostr is locked. Click the Goostr extension icon and unlock.");
  }

  switch (method) {
    case "getPublicKey":
      return getPublicKey(sk);
    case "signEvent": {
      const e = params.event;
      return finalizeEvent(
        { kind: e.kind, content: e.content ?? "", tags: e.tags ?? [], created_at: e.created_at ?? Math.floor(Date.now() / 1000) },
        sk
      );
    }
    case "getRelays":
      return {};
    case "nip04.encrypt": return nip04.encrypt(sk, params.pubkey, params.plaintext);
    case "nip04.decrypt": return nip04.decrypt(sk, params.pubkey, params.ciphertext);
    case "nip44.encrypt": return nip44.encrypt(params.plaintext, nip44.getConversationKey(sk, params.pubkey));
    case "nip44.decrypt": return nip44.decrypt(params.ciphertext, nip44.getConversationKey(sk, params.pubkey));
    default:
      throw new Error(`Unsupported method ${method}`);
  }
}

// ---------- messages from our own pages and content scripts ----------

chrome.runtime.onMessage.addListener((msg, sender, respond) => {
  if (sender.id !== chrome.runtime.id) return;
  (async () => {
    switch (msg?.type) {
      case "nip07":
        // sender.origin comes from the browser, not the page, so it can't be spoofed.
        return { result: await nip07(msg.method, msg.params || {}, sender.origin) };
      case "prompt-decision":
        settle(msg.id, msg.decision);
        return { ok: true };
      case "popup-state": {
        const sk = await getKey();
        const { profile } = await chrome.storage.session.get("profile");
        return {
          npub: sk ? nip19.npubEncode(getPublicKey(sk)) : null,
          profile: profile || null,
          perms: await getPerms(),
          goostrUrl: GOOSTR_URL,
        };
      }
      case "lock":
        await chrome.storage.session.remove(["sk", "profile"]);
        await setBadge();
        return { ok: true };
      case "revoke": {
        const perms = await getPerms();
        delete perms[msg.origin];
        await chrome.storage.local.set({ perms });
        return { ok: true };
      }
      case "open-goostr":
        await chrome.tabs.create({ url: `${GOOSTR_URL}#extension-unlock` });
        return { ok: true };
      default:
        throw new Error("unknown message");
    }
  })().then(respond, (e) => respond({ error: String(e.message || e) }));
  return true;
});